1. Field of the Invention
The invention relates to a laminate substrate with oxygen barrier properties. Such structures of this type are generally useful to prevent spoilage and degradation of food and liquid material stored in containers made from the laminate substrates.
2. Description of the Related Art
Structures for packaging food and liquids, such as orange juice, have typically contained barrier layers made from amorphous nylon or combinations of nylon or ethylene vinyl alcohol (EVOH). Exemplary of such prior art is commonly owned U.S. Pat. No. 5,725,917 (""917) to C. J. Parks, entitled xe2x80x9cBarrier Laminate With Improved Interlayer Adhesionxe2x80x9d and U.S. Pat. No. 6,113,719 (""719) also to C. J. Parks, entitled xe2x80x9cOxygen and Flavor Barrier Laminate Including Amorphous Nylon.xe2x80x9d As an example, a structure based on the ""917 reference, containing approximately 6 lbs/3000 ft2 of amorphous nylon, typically has an oxygen transmission rate of 2.3 cc/100 in2/day/atm at 80% relative humidity and 23xc2x0 C. In order to achieve a higher oxygen barrier, heavier coat weights of an amorphous nylon layer and tie layer must be used. However, use of excessively high coat weights of amorphous nylon layers becomes prohibitively expensive. Also, it might not be possible to apply heavier amorphous nylon coat weights due to limitations in extruder output.
It is also known to use Nylon-MXD6(copyright) manufactured by Mitsubishi Gas and Chemical Corporation as a barrier layer. Nylon-MX6(copyright) has a substantial degree of crystallinity. It is commonly referred to in the art as semi-crystalline nylon. It is made by the condensation of adipic acid and 1,3-benzenedimethanamine. The process forms a compound with different physical and chemical properties as compared to amorphous nylon. Exemplary of such prior art are U.S. Pat. Nos. 5,433,982 (""982) to K. Yamada et al., entitled xe2x80x9cComposite Container Having Barrier Propertyxe2x80x9d, U.S. Pat. No. 5,695,839 (""839) to K. Yamada et al., entitled xe2x80x9cComposite Container Having Barrier Propertyxe2x80x9d, and 6,010,759 (""759) to K. Yamada et al., entitled xe2x80x9cComposite Container Having Barrier Property.xe2x80x9d While the ""982, ""839, and ""759 references employ the use of Nylon-MX6(copyright), they describe a paperboard sheet coated on both sides with polyethylene (PE) which is subsequently laminated with a sheet of co-extruded material including the Nylon-MXD6(copyright) using isocyanate glue or fusing under heat. Therefore, a more advantageous laminate substrate would be one that avoided the use of glue and/or fusing under heat.
It is apparent from the above that there exists a need in the art for a laminate substrate which has a low oxygen transmission rates. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.
The invention provides a laminate substrate with good barrier properties, such as low oxygen transmission rates. An exemplary embodiment comprises a paperboard layer with a heat sealable layer secured substantially adjacent to one side of the paperboard layer. A co-extruded layer is secured substantially adjacent to the other side of the paperboard layer. The co-extruded layer has five layers: a heat sealable layer secured to the paperboard layer, a first tie layer secured adjacent to the heat sealable layer, a semi-crystalline nylon layer secured adjacent to the first tie layer, a second tie layer secured adjacent to the semi-crystalline nylon layer, and a heat sealable layer secured adjacent to the second tie layer. A fourth heat sealable layer is secured adjacent to the co-extruded layer.
The above and other features of the present invention, which will become more apparent as the description proceeds, are best understood by considering the following detailed description in conjunction with the accompanying FIGURE: